This invention relates to carrier wave intelligence transmission systems in general and, more particularly, to apparatus useful in transmitting intelligence from electricity meters over electric power distribution networks to a central site.
The use of electric power lines for meter reading and other communications purposes is well known in the art. It is known that a modulation voltage can be superimposed on a power system voltage to cause wave shape perturbations in the carrier wave. In the embodiment described hereinafter, the carrier wave is the voltage wave of an electrical power distribution system. Communication over electric power distribution lines is useful for signaling, meter reading, and load control, among other uses. Functions such as automatic meter reading require that information passes from the end user back to the central station. See U.S. Pat. Nos. 4,106,007, 4,218,655, and 4,400,688 to Johnston et al, and 4,105,897 to Stratton et al, which patents are incorporated herein by reference.
By way of example, manual reading of electricity meters is highly labor-intensive and its costs are significant. When access to meters is impossible, billings are made on the basis of estimated readings, and such estimated billings often lead to customer complaints.
Currently available electricity meters such as watthour meters work well for their intended purpose, but they must be manually read. For automatic or remote meter reading, a transponder unit must be used with such meters to detect the output of such meters and transmit that information back to a central site. Since there are several different, yet fairly standard meters currently available, it would be desirable to use those meters as part of a meter/transponder package. But inasmuch as there are different meters available, that would appear to require different transponder models for each of the different meter models. Designing, manufacturing and stocking a number of different transponder unit models would, however, be expensive.
Since electricity meters are, in general, exposed to the elements, it is necessary that any meter/transponder package provide some way to protect the electronics of the transponder from the elements. Current meter covers, however, are too small to accommodate the necessary electronics, particularly if the present ability to manually read the meter is to be retained. Space is often at a premium in the locations where electricity meters are disposed, which would seem to dictate the smallest possible size for meter/transponder packages. This presents another problem, however, since the electrical components of transponder units generate a quantity of heat which must be dissipated so that the components will not be damaged. In addition to internally generated heat, the transponder must also be protected from ultraviolet deterioration, humidity, temperature extremes and fluctuations, greenhouse effects, and shock and vibration.
In order to avoid the need to extensively retrain those people who install electricity meters, it would be desirable to have the on-site installation procedures for meter/transponder packages as similar as possible to existing installation procedures for present meters. This would seem to be difficult, however, since the transponder performs a completely different function than that performed by existing manually read meters.
For repair and maintenance purposes it is sometimes necessary to remove the transponder electronics from the meter/transponder package. But it is undesirable to have to remove or replace the meter during that procedure. A transponder built into the meter, however, can only be removed or replaced by removing the meter as well.